Project Summary Dopamine (DA) has been involved in the production of locomotor behaviors throughout evolutionary time. Multiple DA populations in the brain and the spinal cord have been implicated in this process, however several DA populations remain unstudied. Here, we investigate a population of hypothalamic DA neurons that we have recently shown to be critically involved in the production of locomotor behaviors in zebrafish. These neurons are genetically defined by expression of tyrosine hydroxylase-2 (th2). We have shown that ablation of these neurons grossly reduces locomotion and that optogenetic activation increases it. However, the precise nature of the behaviors that are affected by the th2+ neurons is not well understood. To understand how these neurons modulate locomotor behavior, we must know where they send their projections, how their activity modulates those downstream targets, and the precise nature of the behaviors that result from that modulation. The first aim of the proposed work is to identify downstream targets both anatomically and functionally.. The second aim is to precisely identify locomotor patterns regulated by th2+ neurons. This will provide a detailed understanding of the output of the network. These experiments will identify previously unknown mechanisms by which hypothalamic DA neurons modulate locomotor behaviors.